I have been looking over Raid levels over the past 3 days. And have been weighing up the pro/cons of raid controllers hardware/software. I understand that RAID is not a backup solution and I'm perfectly fine with it, though one question still remains.
How does a RAID controller, even Raid 1 to Raid 6 actually detect that a hard disk drive is failing. The research that I have done have showed that most common hard disk drive manufactures use ECC in their hard disk drive design that is suppose to protect against 1 bit failures to an extent 3 bits.
Though when thinking about this, lets say you have Raid (1) and two hard disk drives that are identical. Lets say, data is read from drive 0, and also at the same time from drive 1. Though drive 1 reports a ECC read failure to the Raid Controller.
Now this is the big question, with hardware raid what would the Raid controller do? Its got a signal from the hard disk that the read failed. It can report the hard disk drive as faulty and need replacing.
Does the Raid Controller Seeks to a different hard disk drive for the data until it gets a successfully read from the drive. (Yes, a drive can report read correct and the data can still be corrupted, and RAID does not check polarity or ECC on read)